One of the key components of any computer system is a place to store data. Computer systems have many different places where data can be stored. One common place for storing massive amounts of data in a computer system is on a disk drive, such as a CD-ROM or DVD. The most basic parts of a disk drive are a plastic disk that is rotated, an actuator that moves a transducer to various locations over the disk, and electrical circuitry that is used to write and read data to and from the disk. Some of these drives have read only memory. Others can read the read only memory media and are capable of writing as well. The disk drives also include circuitry for decoding information read from the disk into data so that it can be successfully retrieved from the disk. For writable media, the disk drives also include encoders for encoding the data to a form that can be written to the disk surface so that the data can be retrieved at a later date. A microprocessor controls most of the operations of the disk drive as well as passing the data back to the requesting computer and taking data from a requesting computer for storing to the disk.
In each type of disk drive, the media, which is in the shape of a disk, spins during reading information representing data from the media. The disk also spins when information representing data is written to the drive. There is a constant push to spin the media faster and faster during either the read or write operation so that time required to access data from the disk is shorter or so that the time to write data to the disk is shorter. Some CD-ROM drives and DVD drives spin the media at constant angular velocity. Others vary the spin speeds as a function of the radial position of the data so that the media passes by the transducer at a constant linear velocity. These drives are referred to as constant linear velocity drives and achieve the highest rates of spin when the information representing data is at the outer perimeter of the recording surface. The first CD-ROM drive had a maximum speed of 1×. Current CD-ROM and DVD drives spin at maximum speeds which are multiples of the maximum speed of the 1× CD-ROM drive. Current CD-ROM and DVD drives are 16×, 32×, 40× and 52× which represent the multiple of the original CD-ROM maximum spin speed.
Spinning the disks at higher spin speeds have resulted in problems associated with CD-ROM and DVD drives. An increasing number of broken disks are being found in the high speed CD/DVD drives. Some believe that the disks have disintegrated due to structural defects such as cracks and the like. Another possibility is that the problem is caused when a disk is spinning at a high rate and begins to vibrate on the disk drive spindle.
Analysis of the construction of CD/DVD drives shows that this is a possibility. These disk drives include a disk tray. As the disk tray travels into the drive housing, the motor drive spindle and laser pickup assembly are pivoted up so the motor drive spindle goes through the newly inserted disk. At the same time, an upper spindle body fits over the lower spindle and is held by a magnet in the lower spindle. The result is that the only force holding the disk to the spindle is from the magnet.
If a disk begins to vibrate, at some point the magnet can no longer hold the upper spindle to the lower spindle to retain the disk. When the magnet can no longer hold the vibrating disk, the disk will be released and will spin off of the spindle at a high rate of speed in an uncontrolled direction. It is obvious what happens at this point. The disk slams against the housing and is destroyed. The resulting particles may also lodge within critical mechanisms within the drive and result in ruining the disk drive as well. For example, a plastic portion lodged near a mirror may block the light needed to read from the drive or prevent the mirror movement needed to focus the beam.
Therefore, there is a need for a method and apparatus that can detect vibration in a drive that holds a disk using a magnet having a relatively small force. There is also a need for a method and apparatus that can slow the disk drive in response to a detected vibration condition so as to prevent destruction of the disk in the disk drive.